(1) Field of the Invention
The present invention relates to a system for monitoring an ATM cross-connecting apparatus by inputting a test cell through a normal signal path into the ATM cross-connecting apparatus, and examining the cell after the cell passes through the ATM cross-connecting apparatus.
(2) Description of the Related Art
In ATM (Asynchronous Transfer Mode) networks, virtual paths are cross-connected (switched) by an ATM cross-connecting (virtual path switching) apparatus, which is generally provided in nodes in the ATM network. In each ATM cross-connecting apparatus, a virtual path identifier (VPI) in each cell incoming thereto is rewritten in accordance with a virtual path identifier conversion table, and the cell is cross-connected to another virtual path in accordance with a routing table.
Conventionally, to monitor the normality of the operation of the ATM cross-connecting apparatus, an OAM (Operation, Administration, and Maintenance) cell is transferred as a test cell through a path of the main signal (signal representing information to be transmitted between users of the ATM network), and the content of the transferred OAM cell is examined.
However, conventionally, the content of the above OAM cell as a test cell is written by software in a controller of the ATM cross-connecting apparatus in a node, and is examined by software in the same controller of the ATM cross-connecting apparatus or a controller of another ATM cross-connecting apparatus in the next node to which the OAM cell is transmitted from the ATM cross-connecting apparatus. The testing and monitoring by OAM cell transmission is carried out for every virtual path connected to the ATM cross-connecting apparatus, and the content of information fields of the OAM cells must be various data (bit) patterns. Therefore, a heavy load is imposed on processors in the controller of the ATM cross-connecting apparatuses. In addition, the above various patterns must be stored from the time the patterns are written in the OAM cell until the content of the transferred OAM cell are respectively compared with the stored patterns (examined). Further, the stored patterns may be transferred to the next node when the examination is carried out in the next node. Since the size of the information field is 48 bytes, memory areas of considerable size are required to store the above patterns, and a considerable amount of data (patterns) must be transferred to the next node. Otherwise, the patterns to be written in the OAM cells may be delivered from a central monitoring apparatus to each pair of nodes when the OAM cells are input to an ATM cross-connecting apparatus in one of the pair of nodes and are examined in the other of pair of the nodes. In this case, a large amount of data (patterns) must be delivered to the pair of nodes.